The Bicyclo[2.2.2]octane Motif: A Class of Saturated Group 14 Quantum Interference Based Single-molecule Insulators

Garner, Marc H.; Koerstz, Mads; Jensen, Jan H.; Solomon, Gemma C.

doi:10.26434/chemrxiv.7258214.v1

Cited by 9 publications

(11 citation statements)

References 37 publications

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“…1 For instance, the potential application of molecular wires as single-molecule insulators with even greater insulating properties than vacuum has been pointed out recently. [2][3][4] Moreover, approaches for exploiting the spin-polarization properties of diamagnetic helical molecules, such as proteins or DNA, have been suggested in the past, where chiral-induced spin selectivity can be used to design more efficient water-splitting or memory devices. [5][6][7][8][9][10][11] Besides potential technological applications, the field of molecular electronics is appealing due to its significance for fundamental science, offering insights into molecules under unusual circumstances.…”

Section: Introductionmentioning

confidence: 99%

Toward a First-Principles Evaluation of Transport Mechanisms in Molecular Wires

Kröncke

Herrmann

2020

J. Chem. Theory Comput.

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Understanding charge transport through molecular wires is important for nanoscale electronics and biochemistry. Our goal is to establish a simple first-principles protocol for predicting the charge transport mechanism in such wires, in particular the crossover from coherent tunneling for short wires to incoherent hopping for longer wires. This protocol is based on a combination of density-functional theory with a polarizable continuum model introduced by Kaupp et al. for mixed-valence molecules, which we had previously found to work well for length-dependent charge delocalization in such systems. We combine this protocol with a new charge delocalization measure tailored for molecular wires, and we show that it can predict the tunneling-to hopping transition length with a maximum error of one subunit in five sets of molecular wires studied experimentally in molecular junctions at room temperature. This suggests that the protocol is also well suited for estimating the extent of hopping sites as relevant, e.g., for the intermediate tunneling-hopping regime in DNA. File list (3) download file view on ChemRxiv ms.pdf (1.59 MiB) download file view on ChemRxiv supporting_information.pdf (3.90 MiB) download file view on ChemRxiv cartesian_coordinates.zip (33.23 KiB)

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Section: Introductionmentioning

confidence: 99%

Toward a First-Principles Evaluation of Transport Mechanisms in Molecular Wires

Kröncke

Herrmann

2020

J. Chem. Theory Comput.

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“…This approach gives a qualitatively similar transmission to using periodic Auelectrodes, and allows us to calculate the ballistic current density. 56,85 Both transmission and current density calculations were carried out using DFT with the PBE functional and DZP basis set for all atoms except hydrogen where a SZ basis was used. A Fermi temperature is applied to ensure convergence for systems with vanishing HOMO-LUMO gap, which corresponds to a width of 0.1 in the Fermi function.…”

Section: Methodsmentioning

confidence: 99%

Three Distinct Torsion Profiles of Electronic Transmission Through Linear Carbon Wires

Garner

Bro-Jørgensen²,

Solomon³

2020

Preprint

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<p>The one-dimensional carbon allotrope carbyne, a linear chain of <i>sp</i>-hybridized carbon atoms, is predicted to exist in a polyynic and a cumulenic structure. While molecular forms of carbyne have been extensively characterized, the structural nature is hard to determine for many linear carbon wires that are made in-situ during pulling experiments. Here, we show that cumulenes and polyynes have distinctively different low-bias conductance profiles under axial torsion. We analyze the change of the electronic structure, Landauer transmission, and ballistic current density of the three types of closed-shell molecular carbynes as a function of the torsion angle. Both polyynic, odd-carbon cumulenic,<i> </i>and even-carbon cumulenic carbon wires exhibit helical frontier molecular orbitals when the end-groups are not in a co-planar configuration. This helical conjugation effect gives rise to strong ring current patterns around the linear wires. Only the transmission of even-carbon polyynic wires follows the well-known cosine-squared law with axial torsion that is also seen in biphenyl-type systems. Notably, the transmission of even-carbon cumulenic carbon wires rises with axial torsion from co-planar towards perpendicular orientation of the end-groups. The three distinct transmission profiles of polyynes, odd-carbon cumulenes,<i> </i>and even-carbon cumulenes may allow for experimental identification of the structural nature of linear carbon wires. Their different electron transport properties under axial torsion furthermore underline that, in the molecular limit of carbyne, three different subclasses of linear carbon wires exist.</p>

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“…The methods are described in detail in recent work and in Supporting Information part A. [62][63] Briefly, all molecules are optimized using density functional theory (DFT) with the PBE functional and 6-311G(d,p) basis set as implemented in Gaussian09. [64][65] The optimized structures are rotated without further optimization, thus all degrees of freedom are frozen except for the dihedral angle(s).…”

Section: Scheme 1 Transport Properties Of Organic Molecular Wiresmentioning

confidence: 99%

Simultaneous Suppression of pi- and sigma- Transmission in pi-Conjugated Molecules

Garner¹,

Solomon²

2020

Preprint

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<div><div><div><p>Molecular dielectric materials require ostensibly conflicting requirements of high polarizability and low conductivity. As previous efforts towards molecular insulators focused on saturated molecules, it remains an open question whether pi- and sigma-transport can be simultaneously suppressed in conjugated systems. Here, we demonstrate that there are conjugated molecules where the sigma-transmission is suppressed by destructive sigma-interference, while the pi-transmission can be suppressed by a localized disruption of conjugation. Using density functional theory, we study the Landauer transmission and ballistic current density, which allow us to determine how the transmission is affected by various structural changes in the molecule. We find that in para-linked oligophenyl rings the sigma-transmission can be suppressed by changing the remaining hydrogens to methyl groups due to the inherent gauche-like structure of the carbon backbone within a benzene ring, similar to what was previously seen in saturated systems. At the same time, the methyl groups fulfil a dual purpose as they modulate the twist angle between neighboring phenyl rings. When neighboring rings are orthogonal to each other, the transmission through both pi- and sigma-systems is effectively suppressed. Alternatively, breaking conjugation in a single phenyl ring by saturating two carbons atoms with two methyl substituents on each carbon, results in suppressed pi- and sigma-transport independent of dihedral angle. These two strategies demonstrate that methyl-substituted oligophenyls are promising candidates for the development of molecular dielectric materials.</p></div></div></div>

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The Bicyclo[2.2.2]octane Motif: A Class of Saturated Group 14 Quantum Interference Based Single-molecule Insulators

Cited by 9 publications

References 37 publications

Toward a First-Principles Evaluation of Transport Mechanisms in Molecular Wires

Toward a First-Principles Evaluation of Transport Mechanisms in Molecular Wires

Three Distinct Torsion Profiles of Electronic Transmission Through Linear Carbon Wires

Simultaneous Suppression of pi- and sigma- Transmission in pi-Conjugated Molecules

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